First of all, it would be helpful if the authors would follow the authors guidelines of HESS and provide a detailed individual discussion to the three reviewer comments and not upload a pdf including a response and the revised paper. This is not the correct way for HESS. The discussions will first be considered and then the authors may invited to upload a revised version, but it can also happen that the discussion paper will be rejected.

I think the paper will generally make a valuable contribution to HESS, but additional work and changes are necessary before publication in HESS can be considered. The three reviewer provided detailed and very useful comments to improve the content and presentation of the paper and the authors should consider them very carefully. The authos should in particular focus on the introduction, improve the organization of the paper, and a proper and separate discussion is necessary to allow publication in HESS. This is in particular important as the reader is a bit lost at the end of the results with the different model combinations and parameter and it is unclear what should be considered and done in the next study. I think the combination of a result and discussion section is not appropriate for this paper and the two sections should be separated and the discussion needs to better consider other studies and approaches..
The authors are encouraged to submit a revised paper including detailed answers and responses to all reviewer comments and appropriate changes in the manuscript. The revised paper may then be reconsidered after the major revisions and further review by the editor and reviewers will certainly be necessary.

First of all, it would be helpful if the authors would follow the authors guidelines of HESS and provide a detailed individual discussion to the three reviewer comments and not upload a pdf including a response and the revised paper. This is not the correct way for HESS. The discussions will first be considered and then the authors may invited to upload a revised version, but it can also happen that the discussion paper will be rejected.

I think the paper will generally make a valuable contribution to HESS, but additional work and changes are necessary before publication in HESS can be considered. The three reviewer provided detailed and very useful comments to improve the content and presentation of the paper and the authors should consider them very carefully. The authos should in particular focus on the introduction, improve the organization of the paper, and a proper and separate discussion is necessary to allow publication in HESS. This is in particular important as the reader is a bit lost at the end of the results with the different model combinations and parameter and it is unclear what should be considered and done in the next study. I think the combination of a result and discussion section is not appropriate for this paper and the two sections should be separated and the discussion needs to better consider other studies and approaches..
The authors are encouraged to submit a revised paper including detailed answers and responses to all reviewer comments and appropriate changes in the manuscript. The revised paper may then be reconsidered after the major revisions and further review by the editor and reviewers will certainly be necessary.

I think the paper will generally make a valuable contribution to HESS, but additional work and changes are necessary before publication in HESS can be considered. The three reviewer provided detailed and very useful comments to improve the content and presentation of the paper and the authors should consider them very carefully. The authos should in particular focus on the introduction, improve the organization of the paper, and a proper and separate discussion is necessary to allow publication in HESS. This is in particular important as the reader is a bit lost at the end of the results with the different model combinations and parameter and it is unclear what should be considered and done in the next study. I think the combination of a result and discussion section is not appropriate for this paper and the two sections should be separated and the discussion needs to better consider other studies and approaches..
The authors are encouraged to submit a revised paper including detailed answers and responses to all reviewer comments and appropriate changes in the manuscript. The revised paper may then be reconsidered after the major revisions and further review by the editor and reviewers will certainly be necessary.

General Comments:
You can tell from the authors’ response and the revised manuscript that they really made an effort to take on the suggested changes from the reviews. That is very much appreciated.
The structure of the manuscript has improved considerably. It is much clearer now and the results are explained in a more comprehensible way than before. Also, the authors added more details and explanations of their findings.
Within the text there is still a frustrating amount of spelling, syntax and style errors. Given the amount of co-authors well capable of detecting and correcting these errors, this fact is surprising. It feels like they left these errors for the reviewers to point out and correct.
The story of the abstract could be improved for better readability and the use of the word ‘sensitivity’ should be checked carefully at each occurrence.
For these reasons I recommend this manuscript for publication pending some more revisions.

Specific Comments:
Abstract: The abstract could tell a better story by giving some more information and connecting the individual statements better. You write for example: ‘This method has been used for measuring soil moisture but several other hydrogen pools affect the signal.’
-Which method?
-The ‘but’ does not fit in this sentence
-Why is it a problem that other pools affect the signal?
Maybe it would be better to write something along the lines of ‘Relating cosmic ray neutron counts to the presence of (more or fewer) water molecules within the footprint of the sensor is used for quantifying/measuring the hydrogen content of soil moisture. This is, however, complicated by the fact that several other hydrogen pools affect the signal.’
It would be much easier for the reader to follow.
You should state your intentions early in the abstract: Why have you done this study? You tell us what you have done but with little explanation on your actual goals.
Appropriate would be something like: ‘In order to shed light on the influence of several other hydrogen pools on the measured signal we performed a sensitivity analysis using a neutron transport model with various representations of…’.
Maybe add a concluding statement to the end. ‘While biomass affects … considerably, we found canopy interception to be of minor importance…’.

Page 2, Line 28: ‘…at intermediate spatial scales…’

Page 3, Line 12: ‘For the preparation of cosmic-ray neutron data THE correction for changes in atmospheric water vapor is A STANDARD PROCEDURE along with corrections for temporal variations in barometric pressure and incoming cosmic radiation…’
The native English speakers amongst your co-authors could have done a better job in correcting some of the language and style. Maybe they can carefully read the whole paper one more time.

Page 3, Line 20: What about studies that call for a modification of the calibration function itself (e.g. Iwema et al. 2015, Heidbüchel et al. 2016)? They argue that the function must be adapted to the local environment (more biomass vs. less biomass, higher variability in soil properties with depth vs. lower variability, etc.).

Page 5, Line 5-6: Thermal and epithermal neutron intensities are considered in order to explore the possibilities they offer when observed at the same time (not because they are characterized by very different physical properties – that is the prerequisite for using them in combination).

Page 7, Line 14: Potential problems could arise here. If you use a model to correct/infer pure thermal and pure epithermal neutron intensities, the observed differences can always be explained by this correction model and all the assumptions you made when setting it up.

Page 8, Line 11: ‘…the Danish…’.

Page 9, Line 17: Maybe add some units (m³ m-³)?

Page 11, Line 27: You should definitely add some units (m³ m-³).

Page 11, Line 32: You don’t have to repeat the whole ‘The Gludstedt Plantation reference model’. The second time, just say ‘It’.

Page 13, Line 10: You ‘…rely mostly on the time series measurements…’ for what purpose exactly?

Page 13, Line 13-14: Did you specify this theory anywhere? For example, why does the thermal neutron intensity theoretically decrease with height?

Page 13, Line 14: considerably

Page 14, Line 1: What do you mean by ‘Here’.

Page 14, Line 1: performED

Page 14, Line 1: What do you mean by ‘occasionally’?

Page 14, Line 12-13: Please rearrange the sentence. This way it is confusing.

Page 14, Line 18-20: The two sentences contradict each other (similar vs. more sensitive).

Page 14, Line 20: sensitive

Page 15, Line 5: Additionally, SINCE(?) a considerable range of (what kind of?) values is measured within the footprint of the neutron detector the sensitivity OF NEUTRON INTENSITY to litter and mineral soils dry bulk density is examined…
Carefully check your language again, often the sentences are in the wrong order and therefore very hard to understand.

Page 15, Line 7: What is a ‘higher’ litter layer?

Page 15, Line 9-12: Any ideas on why this is observed?

Page 15, Line 27: ‘we chose’

Page 16, Line 1: So is this change in t/e ratio larger than the noise/measurement uncertainty?

Page 16, Line 4-5: Maybe ‘relation’ is a more appropriate word than ‘sensitivity’. Not only here but throughout the manuscript you should review the use of ‘sensitivity’ which describes in my view the responsiveness of one variable to the change of a certain parameter (mostly used in a modeling context).
Then you could write: The relation of thermal and epithermal neutron intensity to the amount of forest biomass using the forest canopy conceptualization of… is presented…

Page 16, Line 29: ‘provide’

Page 17, Line 15: Are the bi-weekly averages of measurements really much wider? They should be the same, no?

Page 17, Line 27: The area average soil moisture derived from field sampling (and oven-drying)?

Page 17, Line 28: You do have that data to look at. I mean you have the soil moisture profile from the field sampling and the soil moisture content of the litter layer, no? You could mention the observed differences more explicitly.

Page 17, Line 31: ‘AdditionalLY’

Page 18, Line 12: ‘The sensitivity OF neutron…’. Again, this should be picked up by native English speakers.

Most of the comments were addressed in the revision process and the manuscript has been significantly improved accordingly. I have only minor comments that could be considered for final further improvements.

The comments refer to page (p) and line (l) of the paper without track changes or directly to the Author’s comments (AC) provided in the response letter.

Comments

p1,l1. Title has been changed but I regret to say that it is still not clear to me why the Authors want to keep the terms biomass and canopy interception there. The study explores 7 factors. Three showed to be important and 4 not. Biomass is one of the important factors while canopy (at least in this study) is not. I actually agree that biomass and canopy interception are two important hydrological and ecological variables (AC26). But then, why not using the litter layer in the title? It is also an important hydrological and ecological variable and it was even found to affect much more the neutron intensity than the canopy interception. Overall, recalling the title of section 2.3.2 sensitivity to environmental conditions, I think the best title to honor the study could be: Cosmic-Ray neutron transport at a forest field site: sensitivity analysis to different environmental conditions.

p2,l8. Reword This method… in…This neutron intensity has been used for estimating soil moisture…

p2,25. It would be nice concluding the abstract with a nice take-home message e.g., Overall, the results suggest the potentiality to use the ratio signal to discriminate different hydrogen contributions.

p3,l19. Rivera Villarreyes at al., 2011 (not 2013).

p5. I would start the page with the statement of the objectives (i.e., improving the understanding of the environmental effect on Cosmic-Ray neutron intensity based on neutron transport modelling).

p5,l21-22. After all the experimental studies cited in the introduction dealing with biomass and interception (e.g., Baatz et al., 2015; Baroni and Oswald, 2015; Franz et al., 2013; Hawdon et al., 2014), this statement is not justified. Either you state that this is the first MODELLING study which provides a quantitative analysis or you rather remove the sentence.
I also underlines that a recent paper (Tian et al., 2016) was recently published presenting the use of the ratio (bare/moderator counts) for biomass and snow correction. Due to the relevance of the paper in relation of the present study, I think is worth to extend the introduction also by that.

Table 1: You choose (see AC23) the terminology in table 1 because this is used for papers within the same field of research. Still, I think it could be easily improved e.g., “years” instead of “static”, “season” instead of “quasi static” and “hours” instead of Dynamic”.

AC32 i.e., The decreasing epithermal neutron intensity from ground level to 5 m above the ground surface followed by increasing neutron intensities is expected to be a result of measurement uncertainties. I think this statement is worth being included in the manuscript.

the paper improved significantly and you really made an effort to take on the suggested changes from the reviews. That was very much appreciated by the reviewers and myself. I think the paper is closer being published in HESS, but there are still many relevant comments and suggestions by the reviewers that should be considered by the authors before I can make a decision. Please provide a revised version with all changes marked and a detailed response letter to the comments of the reviewers.

thanks a lot for the detailed response and the modification in the paper. I think the paper looks now very good and is in general ready for publication in HESS. When studying the revised version, I found some technical corrections and changes that should be included into the final manuscript:
Table 5 - please remove the left column with the content "Gludsted Plantation models (Fig. 3)". This is not relevant for the table.
Table 6 - please move the unit of the soil moisture the the header row of the table and also provide a header description for the two left columns
In general, most figures could be simplified by removing the symbols for all modelled data. Usually, observations, as they are not continuous, are illustrated as symbols and simulations are illustrated as lines. This would also help your figures as they are very busy with all the symbols for the simulated neutron intensities (fig 2-5, 8, 9).
Please change the extend of the y axis in Figure 7 - all information is situated between 0.8 and 0.85 - so why showing such a wide range? The legend could me move in between the individual graphs.

The cosmic-ray method holds a potential for quantifying canopy interception and biomass. We use measurements and modeling of thermal and epithermal neutron intensity in a forest to examine this potential. Canopy interception is a variable important to forest hydrology, yet difficult to monitor remotely. Forest growth impacts the carbon-cycle and can be used to mitigate climate changes by carbon sequestration in biomass. An efficient method to monitor tree growth is therefore of high relevance.

The cosmic-ray method holds a potential for quantifying canopy interception and biomass. We use...